The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Scroll type machines are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning applications due primarily to their capability for extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps, one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port toward a center discharge port. Typically one of the scroll members is stationary and the other is orbiting. An electric motor is provided which operates to drive the orbiting scroll member via a suitable drive shaft affixed to the motor rotor. In a hermetic compressor, the bottom of the hermetic shell normally contains an oil sump for lubricating and cooling purposes.
Scroll compressors depend upon a number of seals to be created to define the moving or successive chambers. One type of seals which must be created are the seals between opposed flank surfaces of the wraps. These flank seals are created adjacent to the outer suction port and travel radially inward along the flank surface due to the orbiting movement of one scroll with respect to the other scroll. The other type of sealing is one required between the end plate of one scroll and the tip of the wrap of the other scroll. This tip to end plate sealing has been the subject of numerous designs and developments in the scroll compressor field.
One solution to the creation of tip seals has been to machine a groove in the end surface of the wrap and insert a sealing member which can be biased away from the wrap and towards the end plate of the opposite scroll. Unfortunately, due to the machining of the groove, the manufacture of the sealing member and the assembly of these components, the costs associated with incorporating tip seals are not insignificant. Also, the tip seals themselves introduce additional radial and tangential leak paths that are not insignificant, especially in smaller machines. They also introduce additional reliability and durability concerns as they are wear prone elements.
Other designs for scroll compressors have incorporated axial biasing of one scroll with respect to the opposing scroll. The axial biasing operates to urge the tips of the scroll members against their opposing end plate in order to enhance the sealing at the tip of the wrap. The biasing of one scroll member with respect to the opposing scroll member in conjunction with dimensional control of the scroll members themselves has allowed scroll compressors to be manufactured without separate tip sealing members between the tip of the wrap and the opposing end plate.
The dimensional control of the scroll members is capable of producing a scroll wrap which mates with the opposing end plate. When axial biasing is incorporated, the scroll wrap tips are biased against the opposing end plate to provide the necessary sealing. A scroll machine compresses fluid using fluid chambers which move radially inward toward the inner section of the scroll wrap while their volume is decreased to compress the fluid. The compression of the fluid causes the generation of heat such that the scroll wrap is hotter at its radially inner section than at its radially outer section. The difference in temperature of the inner and outer sections of the wrap will result in a difference in the thermal expansion between the inner and outer sections of the wrap and thus the possibility of creating a leak path between the scroll wrap tips and its opposing end plate in at least a portion of the scroll wrap. In addition to creating a leak path between the scroll wrap tips and the opposing end plate, the growth of the inner most section may result in reduced tip to end plate contact bearing area and the possibility of galling the end plate by the scroll wrap is created.
Various methods have been devised to accommodate the unequal growth in the height of the scroll wrap due to thermal expansion. Some designs have provided for machining the scroll wraps such that they are progressively shorter as they approach the central area. In this manner, once the compressor reaches an intended operating temperature, the unequal thermal expansion of the scroll wrap will create a matched height of the scroll wrap for both members. The disadvantages to this design approach include the inherent leak path which is present when the compressor is not operating at the intended operating temperature; as well as determining what the intended operating temperature is when the compressor is in an environment which can drastically change temperatures such as a compressor located outside where temperatures change between winter and summer. Additionally, the manufacturing techniques and controls to produce the tapered wrap can significantly add to the overall cost of the scroll machine. Other designs have proposed variations to the above described wrap height variation such as the radially outer portion being constant in height, the middle portion being progressively shorter and the radially inner portion being constant in height. The disadvantages to these designs are the same as those described above for the progressively shorter designs.
Continued development of scroll machines includes the development of methods for accommodating the difference in thermal expansion of the wraps which is caused by the temperature gradient which occurs between the radially outer portion and the radially inner portion of the scroll machine.
The present disclosure provides the art with a scroll machine which continuously adjusts to the variation of the height of the scroll wrap so that the tip of the wrap and the opposing end plate provide sealing contact between these components during the various operating temperatures experienced by the scroll wraps. The present disclosure utilizes a scroll member which has a first portion which is manufactured from a material having a first coefficient of thermal expansion and a second portion which is manufactured from a material having a second coefficient of thermal expansion. As the temperature of the scroll member changes, the two materials react differently to the temperature change due to the difference in their coefficient of thermal expansion to compensate for the thermal expansion and adjust the relationship between the scroll wrap and the opposing end plate. One aspect of this disclosure is that the cause of the distortion itself, that leads to improper sealing, namely the temperature distribution in the member, can be used to counteract the distortion.
Other advantages and objects of the present disclosure will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.